Climate drives the geography of marine consumption by changing predator communities

Este artículo contiene 7 páginas, 3 figuras, 1 tabla.The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.We acknowledge funding from the Smithsonian Institution and the Tula Foundation.Peer reviewe

Seagrass Herbivory Levels Sustain Site- Fidelity in a Remnant Dugong Population

17 páginas, 5 figuras, 5 tablasHerds of dugong, a largely tropical marine megaherbivore, are known to undertake long-distance movements, sequentially overgrazing seagrass meadows in their path. Given their drastic declines in many regions, it is unclear whether at lower densities, their grazing is less intense, reducing their need to travel between meadows. We studied the effect of the feeding behaviour of a small dugong population in the Andaman and Nicobar archipelago, India to understand how small isolated populations graze seagrasses. In the seven years of our observation, all recorded dugongs travelled either solitarily or in pairs, and their use of seagrasses was limited to 8 meadows, some of which were persistently grazed. These meadows were relatively large, contiguous and dominated by short-lived seagrasses species. Dugongs consumed approximately 15% of meadow primary production, but there was a large variation (3–40% of total meadow production) in consumption patterns between meadows. The impact of herbivory was relatively high, with shoot densities c. 50% higher inside herbivore exclosures than in areas exposed to repeated grazing. Our results indicate that dugongs in the study area repeatedly graze the same meadows probably because the proportion of primary production consumed reduces shoot density to levels that are still above values that can trigger meadow abandonment. This ability of seagrasses to cope perhaps explains the long-term site fidelity shown by individual dugongs in these meadows. The fact that seagrass meadows in the archipelago are able to support dugong foraging requirements allows us to clearly identify locations where this remnant population persists, and where urgent management efforts can be directed.This work was supported by Ravi Sankaran Inlaks Fellowship Program, to ED; Mohammed Bin Zayed Species Conservation Fund, to ED; Ministry of Environment and Forests, CSIC under the PIE programme (Ref: 201330E062), to TAPeer reviewe

Erosion of Traditional Marine Management Systems in the Face of Disturbances in the Nicobar Archipelago

11 páginas, 3 tablas, 2 figurasTo sustainably manage naturally scarce resources, island communities often evolve complex mechanisms including customary laws, belief systems, and reciprocity arrangements among others, to prevent overharvest. Their effectiveness depends largely on the extent to which resource users comply with the rules. We examined patterns of compliance with traditional marine management in the Nicobar Archipelago, India, before, and six years after, the 2004 tsunami. We used interview-based surveys to document marine harvest regulations, and changes in compliance patterns. Our results indicate that pre-tsunami, complex harvest rules existed, including spatio-temporal closures, gear restrictions and species bans; many reefs were subject to multiple, overlapping restrictions. Post-tsunami, compliance weakened considerably; younger individuals (19–35 years) and individuals receiving tsunami aid (boats, gear, etc.) were the most likely non-compliers. Around 84 % of interviewees attributed declining compliance directly to post-tsunami changes in resource availability and a perceived decline in traditional authority. Changes in resource availability can interact strongly with institutional decline, eroding the resilience of traditional management.Peer reviewe

Percentage of primary production grazed by dugongs in six meadows.

<p>This was measured in the period of highest productivity. The numbers on the X-axis correspond to the meadows where measurements were made (1 = Katchall, 2 = Neil1, 3 = Neil2, 4 = Neil3, 5 = Camorta, 6 = Reef).</p

Changes in dugong occupancy (ψ) across the Andaman and Nicobar archipelago over 50 years (1959

<p>–<b>2009).</b> Dugong occupancy (ψ) appears to have been stable in three regions: Ritchie’s Archipelago, Central Nicobars and South Andaman (0.13–0.56). Major historical declines were estimated from north Andaman (from 25% to 0.10%), Little Andaman (5% to 0.01%) and Little and Great Nicobars (20% to 0.06%). It is unclear if dugongs occurred, even in the past, around the Car Nicobar Island. Error bars indicate standard deviation.</p

Effect of dugong herbivory on the shoot density of <i>Halophila ovalis</i>.

<p>Shoot densities were measured inside and outside experimental exclosures at the start of the experiment (T0) and 4 months later (T1). Error bars are standard errors.</p

Description of and limitations about the stated assumptions in parameters of long-term and short-term dynamic occupancy models.

<p>Key: ^a Long-term dynamic occupancy models; ^b Short-term dynamic occupancy models.</p

The location and characteristics of all seagrass meadows surveyed.

<p>The rows highlighted in boldface are meadows with confirmed dugong usage.</p><p>The location and characteristics of all seagrass meadows surveyed.</p

Rate of dugong herbivory measured across six seagrass meadows between February and May.

<p>The numbers on the X-axis correspond to the meadows where measurements were made (1 = Katchall, 2 = Neil1, 3 = Neil2, 4 = Neil3, 5 = Camorta, 6 = Reef). Error bars are standard errors.</p

Differences in dugong mortality records at seagrass meadows (n = 40) over time, showing decline in occupancy or persistence.

<p>The causes of mortality (including shore-stranded or live-caught individuals in fisheries) recorded were mainly entanglement in gillnets and hunting. Live sightings are recorded both from free-ranging and stranded animals.</p